Protein-oligosaccharide conjugates as novel prebiotics

Maintaining a good proportion of gut probiotic bacteria is imperative to health. This may be achieved by consuming “prebiotics,” e.g., galacto-oligosaccharides (GOS) that selectively promote probiotic bacteria, as they often uniquely express transporters for such oligosaccharides. Proteins are an important source for amino acids essential to probiotic bacteria. As most protein digestion products are absorbed in the small intestine, and there is great competition on the residuals by colonic bacteria, amino acids are scarce (<0.01 mM) in the colonic intercellular fluid, thus limiting probiotics' proliferation. However, no existing prebiotic product contains protein. Herein, we propose a new type of prebiotics: protein-oligosaccharide conjugates. These conjugates were designed to be selectively targeted to probiotic bacteria in the colon, for enhancing their competitive advantage over undesired microorganisms. The approach was inspired by active targeting of chemotherapy, achieved by conjugating drugs to ligands, which selectively bind to proteins uniquely expressed on cancer cells; except here, we aimed to promote, not eliminate, the targeted cells. We formed these conjugates by mild Maillard-reaction-based covalent conjugation of GOS to lactoferrin hydrolysate (LFH), formed by peptic digestion, hence it resists gastric digestion. LFH-GOS conjugates comprised 76% ± 1% LFH and 25% ± 4% GOS, and self-assembled into 0.2 to 1.5-μm microparticles. Most of the conjugates' protein content endured simulated gastrointestinal digestion, hence is expected to reach the colon. Remarkably, we found that the growth rate of a model probiotic bacterium (Lactobacillus casei) on the conjugates was double that on the unconjugated components (0.082 and 0.041 h⁻¹, respectively). This study proposes the next generation of prebiotics.